Recordable DVDs are becoming a popular format for storing video and other types of data. These recordable DVDs may be provided in one or more types, including recordable DVDs (DVD/R) and rewritable DVDs (DVD/RW). The former may generally be recorded only once, while the latter may be re-written a number of times. Each of these two types may be provided in one or more formats, including +VR formats (e.g., DVD+R and DVD+RW), as well as −VR formats (e.g., DVD-R and DVD-RW), as well as other customer formats such as DVD Video. The challenge for manufacturers of DVD playback and recording equipment is to provide systems working with all formats in a manner seamless and transparent to the consumer.
The +VR formats were developed by Philips Electronics (Koninklijke Philips Electronics N.V), and have many features analogous to the preceding generation of non-recordable DVDs. Data may be recorded as a stream of MPEG encoded video in successive blocks on the DVD, preceded with a header file of navigation information. For the purposes of this application, these formats will be referred to as DVD+R and DVD+RW formats. The −VR formats were developed by a consortium of companies associated with the original DVD specification, but this latter format has little in common with the prior DVD format. For the purposes of this application, these formats will be referred to as DVD-R and DVD-RW formats or collectively as the DVD-VR formats. Data may be recorded in the −VR format in non-sequential blocks of data, and a file system used to locate blocks of data for playback. A manufacturer faces quite a challenge to provide a system, which may record and play back both +VR format and −VR format DVDs as well as other formats.
Adding to this challenge is the need in the consumer market to provide robust products, which are relatively immune to misuse by the consumer. Unlike PC or computer products, consumer products operate in an environment where the features need to stay simple and user-friendly. The operation of the apparatus needs to be robust, simple, and transparent to the user. One concern in recording DVDs at home is what can happen if the recording process is interrupted, for example, by a power failure, prior to completion of the process. As noted above, both +VR and −VR format systems record video data first, and then record navigation data (or file system data) afterwards. Without this navigation or file system data, the DVD may be difficult if not impossible to play back.
This problem may be a particular concern, as the user may be recording hours of video, and if the process is interrupted, find that most, if not all, of his video data is not accessible. For example, a power failure or the like could interrupt recording of a DVD/RW and thus prevent completion of the recording. The video data is present on the disk, but without updated navigation or file system data, the video data may be unreadable by a Prior Art DVD player. Similarly, in portable applications, such as a DVD/RW camcorder, batteries may be entirely depleted during the middle of shooting video, resulting in the video data being inaccessible to the user. A consumer may not accept such performance characteristics, particularly when comparing performance to such prior art devices as video-cassette recorders (VCRs). If power is lost to a VCR, the last data recorded to the machine is generally still accessible to the consumer—perhaps with the exception of the last seconds of video. However, with a Prior Art DVD recorder, minutes if not hours of video may be lost if the writing function is not completed.
FIG. 1 is a simplified diagram illustrating the relationship between stream information 130 and navigation information 110 in a DVD recorder. Referring to FIG. 1, DVD recording generally involves recording two types of information to the disc, stream information 130 and navigation information 120. Stream information 130 may comprise MPEG data, the actual video data itself. Navigation information 120 may comprise descriptive information, including structures called IFO files and file systems, which allow a playback device to properly locate stream information 130 on the disc.
During real time recording to an optical medium, recording stream information 130 in real-time as it is being input into the device is a common practice. Navigation information 120 may then be generated and written to the disc after the entire stream data 130 has been completely written. Writing of the navigation data 120 is deferred because navigation information 120 cannot be generated without having the entirety of stream information 130. Moreover, it is prohibitively expensive, in terms of access time, to seek to different locations on the disc for writing during the video recording process.
As a result, when a DVD recorder unexpectedly loses power, the recording in progress is often lost because navigation information 120 is never properly flushed to the disc, as illustrated in FIG. 2. In FIG. 2, a partial recording of video data 230 is made, interrupted by some event, such as a loss of power. In this instance, a substantial amount of video data 230 may be recorded, but no navigation information 220 is present. As a result, a Prior Art DVD player cannot read partially recorded video data 230, as the navigation information 220 is not present. If navigation data could be produced, then the partially recorded video data 230 might be recovered.
FIGS. 1 and 2 illustrate the general nature of the power failure or recording interruption problem for a DVD recorder. The specific nature of the problem varies, however, depending upon DVD recorder type (e.g., DVD-R, DVD-RW, DVD+R, DVD+RW, and the like). The following examples illustrate the specific nature of the problems created when a recording interruption event takes place for various different DVD recorder formats.
FIG. 3 is another simplified diagram illustrating how multiple or titles may be recorded to a DVD+RW and how navigation information is then written to the DVD+RW. In this example, each title may represent a separately recorded program segment or video segment. In this example, there are four chapters or titles, T1 through T4. After each title is recorded on the DVD+RW, the Navigation data 120 may be updated to include information describing the location of individual titles within video data 130. Navigation data 120 may also include various menus, which may be displayed to the user when playing back the DVD+RW, as well as pointers to various chapters, as well as any other information used to address video data on the DVD+RW. In addition, Navigation data 120 may include file system data which may be used to locate various files on the DVD+RW for use by a DVD player or for use by a computer when using the DVD+RW as a data disc or the like.
FIG. 4 is a simplified diagram illustrating how a power interruption or other interruption can affect a DVD+RW. In the Example of FIG. 4, recordation of video data is interrupted during recordation of title 4 at point 240, possibly due to a power failure or the like. As a result, the video data is not completely recorded. Moreover, the navigation data 220 may not have been updated (which normally occurs at the end of the recording cycle) and as a result no pointer to title 4 is present. Thus, while the video data for title 4 may be at least partially present on the DVD-RW, no pointer data has been inserted into the navigation data 220, and thus the video data for title 4 cannot be accessed. Access to titles 1–3 may still be possible, but access to the title being recorded during the power failure or other interruption may be denied.
In certain write-once media, prior recordings may also be lost as it becomes difficult to reload the previous state of the disc because of the incomplete information recorded prior to power off. Write-once media (e.g., DVD/R) as the name implies, can only be written to once. Unlike a DVD/RW, which can be written to and overwritten a number of times, write-once media can only be written to a single time.
In some instances, the DVD/R needs to be written to in one single session. If such a DVD/R is interrupted during the writing process, recovering lost video data in a manner to make the DVD/R playable on playback equipment may not be possible since new navigation data may not be able to be written to the DVD/R.
In other types of DVD/R discs, data may be written to the disc only once, but in a number of separate sessions. FIG. 5 is a simplified diagram illustrating how video and navigation data may be written to a write-once media in a number of sessions. As illustrated in FIG. 5, the write-once media may be separated into a limited number of “tracks”, in this case at least two tracks, Track 1 and Track 2. Track 1 may be reserved for navigation data. This navigation data will not be written to the disc until all video data is recorded to the disc in one or more sessions. Once the disc is full or completed, the user may “finalize” the disc, in which case, the navigation information is then created and written to track 1 of the disc as shown.
Navigation information may be created from individual nav data associated with each video segment. In the example of FIG. 5, three video segments, Video 1, Video 2, and Video 3 have been recorded. After each video segment is recorded, associated nav data, Nav1, Nav2, and Nav3, is written onto the disc after its corresponding Video segment. When the disc is finalized, the nav data may then be assembled and recorded into the navigation file on track 1, as illustrated in FIG. 5. Each successive nav data may include nav data from all previous segments. Thus, the Nav2 data may include navigation data for Video1 and Video2, while the Nav3 data may include navigation for Video1, Video2, and Video3. When finalizing the disc, a Prior Art DVD recorder may create the Navigation data from the last Nav data segment, as it includes cumulative pointer and other data for all prior video segments.
FIG. 6 illustrates what happens if power is interrupted or some other event occurs to interrupt a write cycle to a DVD+R recorder. As illustrated in FIG. 6, during the writing of video segment Video3, the cycle is interrupted, perhaps by power failure or the like. As a result, no nav segment Nav3 is created. Moreover, the DVD recorder cannot finalize the disc, as the last nav segment nav3 was never created. As a result, an ordinary DVD player cannot read the DVD, and all video data on the disc may be inaccessible to the user. For consumer grade electronics, this situation is not an acceptable condition.
One prior art solution to this problem is to have a piece of non-volatile memory on the DVD recorder to record state information. The non-volatile memory retains information even when power is disconnected from the device. Once power is restored, the DVD recorder can examine the contents of the non-volatile memory and reconstruct the state of the recording prior to power loss and then reconstruct the navigation data and write it to the DVD.
The primary disadvantage of this solution is cost. Non-volatile memory devices impose a high cost to the DVD recorder. Another disadvantage is that the information in the non-volatile memory is tied intimately with the partial recording of one (or possibly a few) specific DVD discs. For example, if power is lost while recording disc A, then the device will store information about disc A in non-volatile memory. If a disc B is then inserted and information is video recorded onto disc B before recovering the contents of A, then the recorder will lose the ability to recover the data for disc A at a later time.
A brute force search is also a possible technique for recovering data. This brute force approach would require searching every addressable location on a DVD in an attempt to reconstruct the state of the disc prior to power off. However, as most DVDs typically hold over four gigabytes of data, the disadvantage of this technique would be that it is prohibitively slow. The user would become frustrated as the DVD recorder would take a relatively long time (e.g., half-hour) trying to read all four gigabytes of data on the DVD to reconstruct the lost video. The consumer may also think that the device has locked up, and the consumer may cause additional difficulty by turning off the device in the middle of such a brute force recovery mode
Prior Art DVD/RW recorders typically are only able to read previously recorded data in the event of an unexpected power loss, but not the video data being recording at the time of power loss, as illustrated above in connection with FIGS. 3 and 4. Prior Art DVD/R recorders may also lose all of the data on write-once media if recording is interrupted. Consumers expect to be able to recover all video data up to the minute of interruption. Moreover, it is not sufficient in many applications to provide a solution only for one DVD format type, as consumers expect a modern DVD player/recorder to handle most DVD formats. Thus, it remains a requirement in the art to provide a DVD recorder, which can quickly recover lost video data in an efficient and cost-effective manner.